"We all live together and everything," she explains. "It's so different, but it's perfect. They're awesome, and I actually really dig the mom thing."

But don't expect Clarkson to be an overindulgent stepmom. Just like her lyrics repeatedly demonstrate, she is no pushover. (Perhaps that's one reason she has teamed up with State Farm to educate teens about safe driving.)

"I'm quick to go, 'I told you not to touch that!' " she said with a laugh. "We all work really well together, but I'm totally my mom. My mom was a hard mom. I'm probably that mom."

Clarkson will officially earn the title "stepmother" in late October when she swaps vows with Blackstock at their Nashville home.

The Stronger singer has long made it clear she will be a laid-back bride, and it appears she's becoming increasingly blasé as the wedding draws near.

"I'm so over it. It's so overwhelming," she admitted to Seacrest. "We're just doing a lot: touring and the wedding and the Christmas album [out Oct. 29], so I'm over the wedding part."

"It's not a try-hard situation," she says of their relationship. "It's just easy. It's work – after a year and a half that puppy phase [is over] and reality starts to set in – but it's fun work. We're very similar. It's easy."